The Republican from Miami rode a wave of voter discontent last fall, wrestling the GOP nomination away from front-runner and sitting governor Charlie Crist, then going on to win the general election.

In an interview just before Wednesday's ceremony, Rubio said he feels humbled and ready to focus on the job ahead, starting with repealing and replacing the health care law and tackling the national debt and federal spending.

He made light of all the attention he's garnered, including calls for him to run for president. "It's a circus, you guys are part of the circus," he told reporters. "They'll talk about somebody else next week."

The point, though, is he enters with a lot of expectations.

"My expectations are very straightforward," he said. "I ran because I told people I want to be the U.S. Senator from Florida because I believe this country is headed in the wrong direction. I think both parties are to blame. I want to go to Washington, D.C., stand up to the direction it is taking our country and offer a clear alternative. That's what I ran on, that's what I'm going to be for the next six years."

Rubio restated his opposition to the Dream Act — a bill offering a path to legal immigrant status for some children brought to the United States illegally and said the focus should be on border security and employment verification. He said he would support helping a limited segment of young people as part of a modernized immigration system.

And he said he supports rolling back discretionary spending to 2008 and freezing it.

He also said he wants to see a fairer system for prioritizing projects than the "earmark" process that now favors the most influential members of Congress.

Asked where he sees himself fitting in — whether with those Republicans who want to fight every Democratic idea and those who desire bipartisanship — Rubio said: "I think we should only oppose their bad ideas, and they have a lot. That's where I stand on the issues."

He said the two parties have different ideas and the past election showed that people across Florida and the country had a very clear mandate "and that mandate is get control of the spending problem, figure out ways for the federal government to help economic development, not hinder it, and make sure that America continues to be the strongest military power in the world."

"It's humbling," he said. "I don't feel I won anything other than the opportunity to serve."

He was asked about the troubles facing his friend, new U.S. Rep. David Rivera.

"I don't know anything more than what I read in the press accounts and I really don't want to speculate on it. No one wants to read that stuff, but like I said, that will work its way through." He said he still supported Rivera.

Rivera has admitted receiving $137,000 in previously undisclosed loans from a company co-owned by his mother, a company now under criminal investigation over secret payments from the Flagler Dog Track during its campaign to bring slot machines to Miami-Dade parimutuels. Rivera has said he paid the money back.

Regarding the upcoming presidential election, Rubio said he thinks Florida should keep its early primary.

"It's right for Florida for a lot of reasons. What's the point of Florida voters having a primary later in the year that won't mean anything? … I think Florida is the ideal test. There isn't an issue confronting America that they won't have to address in a state like Florida. And as a Republican, I think it behooves us to have an early Republican primary in Florida. Because if a Republican can't win Florida, they can't win the presidency. So we better make sure whoever we nominate is someone who can be palatable to Floridians."

A ceremonial swearing-in took place around 2 p.m. with the oath administered by Vice President Joe Biden. Rubio was surrounded by family, including his mother, Oria, and wife Jeanette and four children: Amanda, Daniella, Anthony and Dominic.

Afterward, Biden told Rubio, "I look forward to working with you."

On Tuesday Rubio announced the opening of five regional offices in Pensacola, Jacksonville, Tampa, Orlando and Miami.